This application is based on patent application Nos. 9-12999, 9-13000, 9-13001, 9-13002, 9-13003, 9-13004, 9-13005, 9-13006, 9-13019, 9-13020, and 9-13021 filed in Japan, the contents of which is hereby incorporated by reference.
This invention relates to an image capturing apparatus capable of picking up a light image of an object by an image pickup device such as CCD (Charge Coupled Device) by photoelectrically converting it into an electric image and storing it in a storage medium such as a hard disk card after applying a specified image processing thereto.
There have been known electronic cameras as image capturing apparatus. Electronic cameras have, as compared with conventional cameras which record light images on silver halide film, an advantage of picking up images of satisfactory quality by suitably applying an image quality processing to the picked up images according to image capturing purposes and types of objects since the quality of captured image can freely be processed. Thus, the digital cameras are used as devices not only for usual picture taking but also for image capturing images such as characters and figures drawn on a white board at, e.g., a conference hall.
In the case that a white board on which characters, figures, etc. are drawn by an electronic camera, the main purpose of the image capturing is to record a representation represented by characters, figures and the like on the white board. Accordingly, it is desirable to apply such a xcex3-correction to the captured image as to enhance the clearness of a representation portion (a portion of characters and figures) by making a white portion (white board portion) white. In this case, since a variation in the character density on the white board and an illuminance nonuniformity are large, it is desirable to correct the illuminance nonuniformity (shading correction) by dividing the captured image into a plurality of blocks in a two-dimensional manner and applying the xcex3-correction block by block.
Specifically, if the white board is assumed to be illuminated by ceiling lights of the room and sunlight coming through the windows, illuminance nonuniformity occurs due to a nonuniform illumination light. By the multiplying effect of this illuminance nonuniformity and a distribution of incident light amount by the so-called law of Cos4xcex8 according to which an image at an off-axis object point which is incident on the entrance pupil of the taking lens at an angle xcfx89, a distribution of the output of the image pickup devices such as CCDs largely varies along horizontal and vertical directions on a sensing surface.
Thus, it is desirable to perform the illuminance nonuniformity correction by dividing the picked image into a plurality of blocks in a two-dimensional manner and by applying the xcex3-correction according to the illuminance in the block for each block. More preferably, it is preferable to set a proper xcex3-characteristic for each block by making the block size as small as possible in order to avoid the creation of a pseudo line at the boundary of the blocks resulting from a sudden change in the xcex3-characteristic in the case that the xcex3-characteristic set for each block largely changes between neighboring blocks.
The xcex3-characteristic for each block used for the xcex3-correction performed block by block can be set using the histogram of level-frequency distribution of the pixel data included, for example, in the block. In other words, when an image of characters, figures or the like drawn on the white board is picked up and a histogram of level-frequency distribution of pixel data constituting the picked image is generated, the generated histogram of level-frequency distribution is normally a two-peak distribution histogram having a convex portion corresponding to the character portion at a dark side and a convex portion corresponding to the white portion (white board) at a bright side. The white level is detected from the convex portion corresponding to the white portion, and the xcex3-characteristic is so set as to convert the pixel data above this white level into pixel data of a predetermined white saturation level.
According to the xcex3-characteristic setting method using the histogram of level-frequency distribution, the set xcex3-characteristic varies according to the number and size of characters included in the block in the case that the picked image is divided into rectangular blocks. If the block size in relation to the character size is improper, a suitable xcex3-characteristic cannot be obtained. For example, if the block size is considerably smaller than a suitable size in relation to the character size, the character portion takes up a large area in the block and an area of the white portion is small. The convex portion corresponding to the white portion of the histogram of level-frequency distribution generated using the pixel data in the block becomes small and it is difficult to determine the white saturation level based on this convex portion. Conversely, if the block size is considerably larger than the suitable size, the convex portion corresponding to the white portion of the histogram of level-frequency distribution generated using the pixel data in the block is sufficiently large. However, since the white portion takes up a large area in the block, the convex portion corresponding to the white portion becomes moderately sloped due to the influence of the nonuniform illuminance. Thus, it is difficult to stably set the white saturation level based on this convex portion.
The character size in a field of the viewfinder easily varies according to the object distance and the image capturing magnification in picture taking. However, it is not preferable that the quality of images obtained by image capturing the same object considerably changes according to the object distance and the image capturing magnification. Accordingly, the block size needs to be set at the specified size in relation to the character size so that a suitable histogram of level-frequency distribution can be obtained.
Further according to the xcex3-characteristic setting method using the histogram of level-frequency distribution, the histogram of level-frequency distribution of the block including both the white board portion and the background portion displays a two-peak distribution having a convex portion corresponding to the white board portion and a convex portion corresponding to the background portion in a white area. Thus, there is a likelihood that the white level is erroneously detected based on the convex portion corresponding to the background portion.
In the case that the background portion is brighter than the white board portion, the white level is detected based on the convex portion corresponding to the background portion and the xcex3-characteristic is set using this white level, the pixel data of the white board portion are not converted into pixel data of specified saturation level (pure white) in monochromatic image capturing. If the xcex3-correction is performed to intensify the black portion to emphasize the characters, the pixel data of the white board portion are converted into black in some cases. This leads to a disadvantage that the white board portion of the block including the background portion turns black. In the case of a color image, if the xcex3-characteristic for the image of any color components is set as above, a part of color components are completely converted into those of the black saturation level. Therefore, a chromatic coloring phenomenon occurs in the white board portion.
In the case that the white board is captured together with its background, the image quality is considerably reduced, making the image hard to be seen if the coloring phenomenon occurs in the white board portion in a boundary area between the white board portion and the background portion during the image processing, namely the illuminance nonuniformity correction. Thus, it is desirable to detect the boundary area between the white board portion and the background portion and to properly perform the image processing in this boundary portion during the illuminance nonuniformity correction.
In a known image forming apparatus such as a digital copying machine, an image processing (xcex3-correction) is applied to an image picked by being photoelectrically converted into an electrical signal using a xcex3-characteristic having a relatively large xcex3-value (xcex3-characteristic having a characteristic similar to a binary processing) in order to make a representation such as characters and/or figures copied on a recording sheet more clear. This xcex3-correction is performed as follows in order to reduce the influence of the nonuniform illuminance. As shown in FIG. 71, a picked image G is divided into a plurality of long rectangular blocks B(1), B(2), . . . B(n) along sub-scanning direction. xcex3-characteristics xcex3(1), xcex3(2), . . . xcex3(n) are set for the respective blocks based on the histogram of level-frequency distributions of the pixel data included in the respective blocks B(r). The xcex3-correction is applied to the pixel data in each block B(r) (r=1, 2, . . . n) using the xcex3-characteristic xcex3(r) corresponding to this block. By this xcex3-correction, the white portion above a specified level is uniformly converted into an image of a specified white color, and the character portion (black portion) below the specified level is uniformly converted into an image of a specified black color. Accordingly, an image which could have been obtained by a binary processing can be obtained.
Japanese Unexamined Patent Publication No. 6-113139 discloses an image binary processing apparatus. This apparatus divides a picked image into a plurality of partial images; generates a histogram of level-frequency distribution of pixel data included in the block for each of a selected partial image block (object partial image block) and a plurality of partial image blocks neighboring the object partial image block; sets a threshold value for the object partial image block by neural network using the histogram of level-frequency distribution data; and applies a binary processing to the pixel data in the object partial image block using this threshold value.
Since the object distance and the copying magnification are substantially constant, the picked image is normally divided by blocks of predetermined size during the xcex3-correction in the known digital copying machine. The binary processing technique disclosed in the above publication mainly concerns a binary processing in a copying machine and a facsimile machine. This publication does not disclose any measure to deal with a change in the shape of the histogram of level-frequency distribution when the character density in the block varies according to the object distance and image capturing magnification. Accordingly, the illuminance nonuniformity correction may not be performed even if the conventional xcex3-correction technique is applied to digital cameras. According to this xcex3-correction technique, the picked image is divided by the blocks only along sub-scanning direction. Thus, even if this technique is applied to a picture image where the illuminance nonuniformity occurs in a two-dimensional manner, it is difficult to effectively correct the illuminance nonuniformity along main scanning direction.
On the other hand, according to the binary processing technique disclosed in the above publication, a picked image is divided by a plurality of blocks arranged as in a matrix and the binary processing is applied to the pixel data every block. This technique is effective as a method for correcting the illuminance nonuniformity of a picture image. However, since the histogram of level-frequency distribution of the pixel data is generated every block and the threshold value of the binary processing is set by neural network using the histogram of level-frequency distribution data, a complicated and cumbersome calculation is disadvantageously required to set the threshold value. If the block size is set too small, the histogram of level-frequency distribution of the pixel data is improper and a suitable threshold value cannot be set. Further, since a long time is disadvantageously required for the calculation due to a huge number of blocks, there should be a limit in the number of blocks. Further, a calculation made to avoid the discontinuity of the image quality resulting from a difference between the processings applied to the blocks using different xcex3-characteristics is not easy.
The known digital copying machine and the image binary processing apparatus disclosed in the above publication mainly concern the binary processing performed in the copying machine and the facsimile machine. The background portion image is picked substantially at the same white level as the white portion of a document in view of the construction of the apparatus. The aforementioned coloring phenomenon quite seldom occurs and, accordingly, presents no problem. Thus, a problem of the coloring phenomenon in the boundary area between the white board portion and the background portion is not considered at all and, hence, there is no indication or disclosure concerning this problem.
In the case that the picked image is a color image comprised of three primary color components R (red), G (green), B (blue), the aforementioned illuminance nonuniformity correction needs to be applied to the image of each color components since the xcex3-correction needs to be applied to the image of each color components.
If an object is a white board which is relatively pure white and on which black characters are drawn, a histogram of level-frequency distribution is generated using an image of green components having many luminance components out of the images of the respective color components R, G, B constituting a color image as a whole, and the white portion (the white board portion) can be detected based on the shape of this histogram of level-frequency distribution. The illuminance nonuniformity correction can be performed by using the xcex3-characteristic set for the image of green components for the xcex3-correction for the images of red and blue components.
Specifically, if the histogram of level-frequency distribution is generated using the pixel signals of green components, and an input level W is set as a white saturation level of the xcex3-characteristic based on this histogram of level-frequency distribution, the pixel signals of green components above the input level W are all converted into the pixel signals of the same saturation level. Since the white board is nearly pure white and the color components R, G, B of the image of the white board portion are substantially at the same level, the pixel signals of red and blue components above the input level W are all converted into those of the same saturation level even if the same xcex3-characteristic is applied thereto. Thus, the image of the white portion having the levels of the color components R, G, B above the input level W can be uniformly converted into an image of a specified white color.
However, if the white board has a tint, the color components R, G, B of the image of the white board portion are not at the same level. Thus, if the xcex3-characteristic set using the image of green components is applied to the pixel signals of red and blue components, the level balance of the color components R, G, B changes and the tint stands out more. Specifically, if the levels of the respective color components R, G, B are: DR, DG, DB (DG greater than DR greater than DB), the color components are all converted to the saturation level, i.e., a specified white color in a portion having such color components: W less than DR, W less than DG, W less than DB. For example, in a portion having such color components: DB less than DR less than W, Wxe2x89xa7DG, only the green components are converted into the saturation level and the red and blue components are converted to a specified level lower than the saturation level. Accordingly, the image in this portion is converted to, e.g., the one of a striking yellow green color having strong green components. As a result, the illuminance nonuniformity correction causes a problem of coloring the white portion.
Generally, the white board is seldom captured in pure white because of a variety of conditions including the color temperature of the illumination light and the smear on the white board. Thus, it is necessary to perform the illuminance nonuniformity correction while taking a measure to prevent the aforementioned problem in color image capturing. The known digital copying machine and the image binary processing apparatus disclosed in Japanese Unexamined Patent Publication No. 6-113139 mainly concerns a binary processing in a copying machine and/or a facsimile machine, and are premised on that a document image is picked up in the form of a monochromatic image. They neither disclose nor indicate the illuminance nonuniformity correction technique for a color image and the problem in the illuminance nonuniformity correction of the color image.
When characters and/or figures drawn on a white board in a conference hall are to be captured by an electronic camera provided with a built-in flash, the built-in flash is often automatically fired because only an insufficient amount of illumination light is normally available, thereby resulting in flash image capturing. If the white board is captured from front in such flash image capturing, the flash light is regularly reflected by the white board and the characters or the like drawn on the white board become white by this reflection light, with the result that an image having a low representation value is obtained by the image capturing. Even if the flash is not fired, the characters or the like drawn on the white board become white by the regularly reflected illumination light in such an image capturing position where the illumination light such as the ceiling light and sunlight is regularly reflected by the white board. Thus, this case also leads to a similar reduction in the image quality. If the aforementioned illuminance nonuniformity correction is performed in the image processing, an accurate histogram of level-frequency distribution cannot be generated in the block including the regularly reflected light. Therefore, the illuminance nonuniformity correction cannot be effectively performed, and the regularly reflected light adversely affects the blocks which are around this block, but do not include the regularly reflected light. As a result, the image quality and the representation value are considerably reduced.
In known image forming apparatuses such as digital copying machines, if illumination light is regularly reflected by a document, the density of characters or the like written on the document is considerably reduced by this regularly reflected light and a document image cannot be accurately picked up. In order to prevent such a problem, a technique for detecting the illumination light regularly reflected by the document was developed.
This detection technique is such that the histogram of level-frequency distribution of pixel signals picked by image pickup devices such as CCDs every line of a sensor is generated and the presence or absence of the regularly reflected light is judged based on the shape of the histogram of level-frequency distribution. More specifically, in the case that the regularly reflected light is included, the pixels having received the regularly reflected light output the pixel signal of saturated level. Accordingly, the presence or absence of the regularly reflected light is judged by, for example, judging whether the frequency at the saturation level of the histogram of level-frequency distribution exceeds a specified threshold value.
Since a document is illuminated by an artificial light source under a specified condition in digital copying machines, the regularly reflected light can be satisfactorily detected by the line detection of the sensor. However, with electronic cameras, the illumination condition of the illumination light is not constant and an external light such as a sunlight is incident on the white board as a spot light and regularly reflected. Thus, if the detection is made every line as with the known method for detecting the regularly reflected light in the digital copying machines, it is difficult to securely detect a spot regularly reflected light and a sufficiently satisfactory detection accuracy cannot be ensured.
The binary processing technique disclosed in Japanese Unexamined Patent Publication No. 6-113139 also mainly concerns a binary processing in copying machines and facsimile machines, and does not at all disclose the aforementioned problem of the regularly reflected light peculiar to the image capturing of the digital camera and the method for avoiding such a problem.
In the case that a representation such as characters and/or figures drawn on a white board is captured in an oblique direction with respect to the white board in, e.g., a conference hall due to a seating position of an image capture person, a perspective geometric distortion is created in a captured image because the representation such as characters cannot be entirely in focus. Such a distortion reduces the readability of the representation. In order to solve this problem, an electronic camera could be proposed which is able to capture an object image while correcting the perspective image distortion created therein, in other words, to perform image capturing while correcting an obliquely captured image into a pseudo front image (image seen as if it were captured from front).
This electronic camera is such that an image capturing magnification in each pixel position within a field is calculated using an angle of inclination of an object with respect to the camera, a focal length of the taking lens and an object distance, and that a geometric image distortion is corrected by enlarging or reducing a part of the captured image based on the image capturing magnifications. For example, in the case that the white board is captured in an oblique direction from the left, a partial image at the left side of the center of the field is close to the camera and a partial image at the right side thereof is away from the camera. Thus, the obliquely captured image is corrected into a pseudo front image by reducing the left side image and enlarging the right side image.
Generally, a white board in a conference hall is hardly illuminated at a uniform illuminance and can be seldom captured in a front position. Therefore, an image processing adopting both the illuminance nonuniformity correcting function and the oblique image correcting function is applied to an image captured in such a scene.
In this case, if the oblique image correction is performed after the illuminance nonuniformity correction, the number of characters in the blocks (character density of the blocks) varies depending on the positions of the blocks since the image capturing magnification of the obliquely captured image and the character size differ within the field. Accordingly, the shape of the histogram of level-frequency distribution generated for each block largely varies among the blocks. Thus, the white level becomes discontinuous due to a difference of the xcex3-characteristics between neighboring blocks, making it difficult to perform a proper illuminance nonuniformity correction and, depending on a case, leading to the creation of a pseudo line at the boundary of the blocks.
On the other hand, there are some cases where the illuminance nonuniformity correction cannot be properly performed even if the illuminance nonuniformity correction is performed after the oblique image correction. Specifically, pixel data are missing in a portion of an image where the oblique image is corrected by the reduction processing, and dummy data are filled in this portion. Accordingly, if the histogram of level-frequency distribution of the block including the dummy data is generated during the illuminance nonuniformity correction, the obtained histogram of level-frequency distribution cannot be accurate because of the presence of the dummy data. This leads to an improper xcex3-characteristic for the block including the dummy data. Thus, the xcex3-correction cannot be properly applied to the image in this block, and the white level becomes discontinuous between neighboring blocks, thereby creating a pseudo line at the boundary of the blocks.
For the block including the portion where the pixel data are missing, there is a method for generating the histogram of level-frequency distribution using only effective pixel data. However, this method has a disadvantage that an effective xcex3-characteristic cannot be obtained for a block having a small number of effective pixel data despite a complicated processing of extracting the pixel data.
The above problem occurs not only in the case of correcting the geometric distortion of the image obtained by image capturing the object in the oblique direction, but also in the case of correcting a geometric distortion resulting from the characteristic of an image pickup optical system.
The binary processing technique disclosed in Japanese Unexamined Patent Publication No. 6-113139 mainly concerns a binary processing in copying machines and facsimile machines similar to the known digital copying machines. This apparatus is not provided with the oblique image correcting function since a document image is not picked up in an oblique direction because of its construction. Accordingly, this apparatus does not experience the aforementioned problem arising when both the illuminance nonuniformity correction and the oblique image correction are performed. Therefore, this publication neither discloses nor indicates such a problem.
It is an object of the present invention to provide an image capturing apparatus which has overcome the problems residing in the prior art.
It is another object of the present invention to provide a method for processing image data generated by an image pickup device which has overcome the problems residing in the prior art.
According to an aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; a block setter which sets a plurality of blocks over the number of pixel data; a first xcex3-characteristic setter which sets a first xcex3-characteristic for pixel data at a center position of each block based on pixel data included in its block; a second xcex3-characteristic setter which sets second xcex3-characteristics for pixel data at other positions than the center position of each block based on set first xcex3-characteristics; and a xcex3-characteristic corrector which corrects pixel data of each block in accordance with the set first and second xcex3-characteristics.
According to another aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; a block setter which sets a plurality of blocks over the number of pixel data; a xcex3-characteristic setter which sets a xcex3-characteristic for each block based on pixel data included in its block; a xcex3-characteristic corrector which corrects pixel data of each block in accordance with the set xcex3-characteristic; and an image geometric distortion corrector which corrects a geometric distortion of the image data having been corrected by the xcex3-characteristic corrector.
According to another aspect of the present invention, an image capturing apparatus comprising: a taking lens having changeable image capturing magnifications; a detector which detects an image capturing magnification of the taking lens; an image pickup device which photoelectrically picks up a light image of an object passed through the taking lens to generate image data including a number of pixel data; a block setter which sets a plurality of blocks over the number of pixel data; a block size setter which sets a size of each block based on a detected image capturing magnification; a xcex3-characteristic setter which sets a xcex3-characteristic for each block; and a xcex3-characteristic corrector which corrects pixel data of each block in accordance with the set xcex3-characteristic.
According to another aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; an image geometric distortion corrector which corrects a geometric distortion of the image data; a block setter which sets a plurality of blocks over the image data having been corrected by the image geometric distortion corrector; a xcex3-characteristic setter which sets a xcex3-characteristic for each block based on pixel data included in its block; and a xcex3-characteristic corrector which corrects pixel data of each block in accordance with the set xcex3-characteristic.
According to another aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; and an image geometric distortion corrector which corrects a geometric distortion of the image data by applying a reduction processing to a specified portion of the image data, and filling dummy pixel data in a portion where pixel data is to be lost due to the reduction processing.
According to another aspect of the present invention, an image capturing apparatus comprising: a color image pickup device which photoelectrically picks up a light image of an object to generate image data of three primary color components; a white level calculator which calculates a white level for an image of each color component based on image data of its color component; a xcex3-characteristic setter which sets a xcex3-characteristic for an image of each color component to convert image data of its color component above the calculated corresponding white level to a white saturation level; and a xcex3-characteristic corrector which corrects image data of each color component in accordance with the set xcex3-characteristic.
According to another aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; a block setter which sets a plurality of blocks over image data generated by the image pickup device; a reference histogram generator which generates a reference histogram for each block, the reference histogram representing a level-frequency distribution of pixel data included in its block; and a block extractor which extracts a boundary block including pixel data of a boundary between a main subject image and a background image based on the generated reference histogram.
According to another aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; a flash device which emits flash light to the object; an illuminance nonuniformity corrector which performs an illuminance nonuniformity correction to image data generated by the image pickup device; and a controller which controls the flash device to prohibits emission of flash light when the illuminance nonuniformity correction is designated.
According to another aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; a block setter which sets a plurality of blocks over image data generated by the image pickup device; a reference histogram generator which generates a reference histogram for each block, the reference histogram representing a level-frequency distribution of pixel data included in its block; a detector which detects based on a reference histogram for each block whether its block has pixel data in connection with light regularly reflected at a main subject; and an operator which performs a specified operation when there is detected to be a block having pixel data in connection with light regularly reflected at the main subject.
According to another aspect of the present invention, an image capturing apparatus comprising: an image pickup device which photoelectrically picks up a light image of an object to generate image data including a number of pixel data; a taking lens which focuses the light image onto an image pickup surface of the image pickup device; a distance meter which meters a distance to the object; a calculator which calculates a distribution of image capturing magnifications within a specified portion of the surface of the object based on a focal length of the taking lens and an object distance metered by the distance meter; a block setter which sets a plurality of blocks over image data generated by the image pickup device, the plurality of blocks respectively having different sizes in accordance with image capturing magnifications; a xcex3-characteristic setter which sets a xcex3-characteristic for each block based on pixel data included in its block; a xcex3-characteristic corrector which corrects pixel data of each block in accordance with the set xcex3-characteristic; and an image geometric distortion corrector which corrects, based on a calculated distribution of image capturing magnifications, a geometric distortion of xcex3-characteristic corrected image data that is caused by an oblique image capture.
According to another aspect of the present invention, a method for processing image data generated by an image pickup device, the image data including a number of pixel data, the method comprising the steps of setting a plurality of blocks over the number of pixel data; setting a first xcex3-characteristic for pixel data at a center position of each block based on pixel data included in its block; setting second xcex3-characteristics for pixel data at other positions than the center position of each block based on set first xcex3-characteristics; and correcting pixel data of each block in accordance with the set first and second xcex3-characteristics.
According to another aspect of the present invention, a method for processing image data generated by an image pickup device, the image data including a number of pixel data, the method comprising the steps of setting a plurality of blocks over the number of pixel data; setting a xcex3-characteristic for each block based on pixel data included in its block; correcting pixel data of each block in accordance with the set xcex3-characteristic; and correcting a geometric distortion of the xcex3-characteristic corrected image data.
According to another aspect of the present invention, a method for processing image data which is generated by an image pickup device photoelectrically picking up a light image of an object through a taking lens having changeable image capturing magnifications, the image data including a number of pixel data, the method comprising the steps of: detecting an image capturing magnification of the taking lens; setting a plurality of blocks over the number of pixel data; setting a size of each block based on a detected image capturing magnification; setting a xcex3-characteristic for each block; and correcting pixel data of each block in accordance with the set xcex3-characteristic.
According to another aspect of the present invention, a method for processing image data generated by an image pickup device, the image data including a number of pixel data, the method comprising the steps of: correcting a geometric distortion of the image data; setting a plurality of blocks over the corrected image data; setting a xcex3-characteristic for each block based on pixel data included in its block; and correcting pixel data of each block in accordance with the set xcex3-characteristic.
According to another aspect of the present invention, a method for processing image data generated by an image pickup device, the image data including a number of pixel data, the method comprising the steps of: correcting a geometric distortion of the image data by applying a reduction processing to a specified portion of the image data, and filling dummy pixel data in a portion where pixel data is to be lost due to the reduction processing.
According to another aspect of the present invention, a method for processing image data of three primary color components generated by a color image pickup device, the method comprising the steps of: calculating a white level for an image of each color component based on image data of its color component; setting a xcex3-characteristic for an image of each color component to convert image data of its color component above the calculated corresponding white level to a white saturation level; and correcting image data of each color component in accordance with the set xcex3-characteristic.
According to another aspect of the present invention, a method for processing image data generated by an image pickup device, the image data including a number of pixel data, the method comprising the steps of: setting a plurality of blocks over image data; generating a reference histogram for each block, the reference histogram representing a level-frequency distribution of pixel data included in its block; and extracting a boundary block including pixel data of a boundary between a main subject image and a background image based on the generated reference histogram.
According to another aspect of the present invention, a method for controlling an image capturing apparatus provided with an illuminance nonuniformity corrector for performing an illuminance nonuniformity correction to obtained image data, and a flash device for emitting flash light to an object, the method comprising the step of prohibiting flash light emission of the flash device when the illuminance nonuniformity correction is designated.
According to another aspect of the present invention, a method for processing image data generated by an image pickup device, the image data including a number of pixel data, the method comprising the steps of: setting a plurality of blocks over the number of pixel data; generating a reference histogram for each block, the reference histogram representing a level-frequency distribution of pixel data included in its block; detecting based on a reference histogram for each block whether its block has pixel data in connection with light regularly reflected at a main subject; and performing a specified operation when there is detected to be a block having pixel data in connection with light regularly reflected at the main subject.
According to another aspect of the present invention, a method for processing image data which is generated by an image pickup device photoelectrically picking up a light image of an object through a taking lens having a focal length, the image data including a number of pixel data, the method comprising the steps of: metering a distance to an object; calculating a distribution of image capturing magnifications within a specified portion of a surface of the object based on a focal length of the taking lens and a metered object distance; setting a plurality of blocks over the number of pixel data, the plurality of blocks respectively having different sizes in accordance with image capturing magnifications; setting a xcex3-characteristic for each block based on pixel data included in its block; correcting pixel data of each block in accordance with the set xcex3-characteristic; and correcting, based on a calculated distribution of image capturing magnifications, a geometric distortion of xcex3-characteristic corrected image data that is caused by an oblique image capture.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.